The present disclosure relates to a multilayer ceramic electronic part to be embedded and a printed circuit board having the multilayer ceramic electronic part embedded therein.
As an electronic circuit has undergone high densification and high integration, mounting space on the printed circuit board for mounting passive elements has become insufficient. To overcome this problem, an embedded device, a part embedded in a board, has been under development. In particular, various methods to embed a multilayer ceramic electronic part, which is used as a capacitive component, in a board have been proposed.
As an example of a method of embedding a multilayer ceramic electronic part in the board, the material of a board itself may be used as the dielectric material for a multilayer ceramic electronic part and copper wire or the like may be used as an electrode for the multilayer ceramic electronic part. Alternatively, a polymer sheet having a high permittivity or a thin film dielectric may be formed in a board to form a multilayer ceramic electronic part to be embedded, or a multilayer ceramic electronic part may be embedded in a board.
Typically, a multilayer ceramic electronic part includes a plurality of dielectric layers formed of a ceramic material, and internal electrodes each interposed between the dielectric layers. By disposing such a multilayer ceramic electronic part in a board, a multilayer ceramic electronic part to be embedded having high capacitance can be implemented.
In order to manufacture a printed circuit board having a multilayer ceramic electronic part embedded therein, after a multilayer ceramic electronic part is inserted in a core board, via holes are to be made in a top layer plate and a bottom layer plate using laser in order to connect board wirings to external electrodes of the multilayer ceramic electronic part. The laser processing contributes to a significant increase in manufacturing costs of the printed circuit board.
Further, since a multilayer ceramic electronic part is embedded in a core part in a board, a nickel/tin (Ni/Sn) plating layer is not necessary on external electrodes, unlike a typical multilayer ceramic electronic part which is mounted on a surface of a board.
Since an external electrode of a multilayer ceramic electronic part to be embedded is electrically connected to a circuit in the board through a via formed of copper (Cu) material, a copper (Cu) layer is necessary on the external electrode instead of the nickel/tin (Ni/Sn) layer.
In general, although the external electrode contains copper (Cu) as a main component, it also contains glass which absorbs laser during laser processing used to form a via in the board. Therefore, the processing depth of the via cannot be adjusted.
For this reason, a separate copper (Cu) plating layer is formed on the external electrode of the multilayer ceramic electronic part to be embedded.
The multilayer ceramic electronic part is embedded in a printed circuit board used in memory cards, PC main boards, and various radio frequency (RF) modules, such that the size of a product may be significantly reduced compared to when a multilayer ceramic electronic part is mounted on a board.
Further, the multilayer ceramic electronic part to be embedded may be disposed significantly close to an input terminal of an active element such as a microprocessor unit (MPU), such that interconnect inductance associated with the length of conduction lines may be reduced.
Such reduction in inductance obtained in the multilayer ceramic electronic part to be embedded is merely caused by a decrease in the interconnect inductance achieved by the inherent arrangement in which the parts are embedded in the board. Accordingly, equivalent series inductance (ESL) characteristics of the multilayer ceramic electronic part to be embedded still need improvement.
In general, in the multilayer ceramic electronic part to be embedded, a current path in the multilayer ceramic electronic part needs to be shortened in order to lower the ESL characteristics.
However, it is not easy to shorten the current path, because a plating solution may permeate the external electrode if a separate copper (Cu) plating layer is formed on the external electrode of the multilayer ceramic electronic part to be embedded.